Powder coating apparatus producing a flat powder spray

ABSTRACT

A nozzle for a powder spray gun having an elongated orifice from which a gas suspension of the powder is discharged in a flat, fanlike spray. The nozzle includes means adjacent the orifice inside the nozzle to force convergence of the suspension at the orifice and means in the flow of the suspension rearwardly from orifice cooperating with the means forcing convergence of the suspension to promote uniformity of powder distribution in the spray. The powder spray gun may include a suitable electrode adapted for connection to a high-voltage source to charge and promote the deposition of the powder particles in the spray.

United States Patent FLAT POWDER SPRAY 22 Claims, 5 Drawing Figs.

[52] U.S.Cl 317/3,

[51] Int. Cl .1 1805b 1/04,

[50] Field of Search ..239/590, 15

[56] References Cited UNITED STATES PATENTS 398,327 2/1889 De Vars 317/3X Primary Examiner- Lee T Hix Attorneys-Merrill N. John, Harry E.Downer, David H.

Badger and Verne A. Trask.

ABSTRACT: A nozzle for a powder spray gun having an elongated orificefrom which a gas suspension of the powder is discharged in a flat,fanlike spray. The nozzle includes means adjacent the orifice inside thenozzle to force convergence of the suspension at the orifice and meansin the flow of the suspension rearwardly from orifice cooperating withthe means forcing convergence of the suspension to promote uniformity ofpowder distribution in the spray. The powder spray gun may include asuitable electrode adapted for connection to a high-voltage source tocharge and promote the deposition ofthe powder particles in the spray.

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IN VENT( )R.

DAVID D HARROLD RICHARD O. PROBST PATENTEUJUNZSIQYI 3,590,318

SHEET 2 OF 2 INVIENIYJR. DAVlD 0. HARROLD BY RICHARD o. PROBST POWDERCOATING APPARATUS PRODUCING A FLAT POWDER SPRAY This is a continuationof application Ser. No. 579,233, filed Sept. 14, 1966, now abandoned.

This invention relates to apparatus for use in spraying powders to formcoatings on the surfaces of articles and is primarily concerned with,although not limited to, apparatus in which electrostatic forces aid inthe formation of the desired coating. It is known to form a suspensionof powder in air or other gas and to discharge the suspension through anozzle to produce a spray directed toward the surface to be coated, andit is also known to create between the nozzle and the surface beingcoated an electrostatic field-promoting deposition of the powder on suchsurface. So far as I am aware, nozzles heretofore used in theapplication of powder coatings have produced a generally conical spraywhich, when directed against an extended flat surface, deposits thepowder in a circular or annular pattern. In spray coating, whether withliquids or powders, sprays which form circular or annular depositedpatterns are in general less desirable than flat or fan-shaped sprayswhich form elongated, relative narrow patterns.

When fan-shaped sprays are used in the coating of article surfaces, theusual practice involves moving either the spray gun or the article insuch a manner that the spray lies in a plane transverse to the directionof relative movement. To avoid the production of streaks in the coating,it is therefore desirable that the distribution of spray particlesacross the width of the spray be reasonably uniform. In the spraying ofliquid-coating materials under high hydraulic pressure, fanshaped sprayspossessing satisfactorily uniform distribution of the spray particleshave been produced by nozzles having a supply passage which terminatesin a concave, hemispherical surface intersected by a groove of V-shapedin cross section extending diametrically across the end of the nozzle toform an elongated discharge orifice. However, when a nozzle of thattype, appropriately changed in dimensions, is used to discharge agaseous powder suspension it is found that the powder is heavilyconcentrated in the middle portion of the spray and is not uniformlydistributed across the major portion of the sprays width, as is the casewith liquids.

Our invention springs from the discovery that the distribution of powderin a spray discharged from an elongated nozzle opening can be controlledby providing in the passage leading to such opening a transverse pin orsimilar obstruction disposed parallel to the longest dimension of theopening and a short distance rearwardly from the opening; and a nozzlein accordance with the invention therefore embodies such an obstruction.Preferably, the orifice is formed by the intersection of a hemisphericalsurface at the end of the nozzle passage and a V-shaped slot extendingacross the end of the nozzle. When the nozzle is to be used in anelectrostatic system, it may incorporate a spray-charging electrodedesirably in the form of a semiconductive coating applied to a nozzlebody of insulating material and terminating in an annular edgesurrounding but spaced laterally outwardly from the discharge orifice.Accord ing to one feature of the invention, such an electrode may besupplemented with an auxiliary electrode, which can take various forms.

Further features of the invention will become apparent from thefollowing more detailed description and from the accom panying drawing,in which:

FIG. 1 is an illustration, partially diagrammatic in character, of anelectrostatic powder-coatin g apparatus including a spray gun, parts ofwhich are broken away and shown in vertical section;

FIG. 2 is an end elevation of the nozzle embodied in the gun of FIG. 1;

FIG. 3 is a plan view of the nozzle;

FIG. 4 is an axial section through a nozzle provided with a platelikeauxiliary electrode disposed in the nozzle orifice; and

FIG. 5 is a plan view, in panial section, showing a nozzle provided witha different form of auxiliary electrode.

fitting 17 to a supply conduit 18, conveniently a flexible 0 plastictube, leading from a means 19 for delivering a suspension of the powderin a gaseous medium. Details of the means 19 are not illustrated, asvarious forms of such means are well known.

The tube 13 houses a resistor 21 the rear end of which iselectricallyconnected to a flexible cable 22 secured to the rear plug byan appropriate fitting 23 and extending therefrom to the ungroundedterminal of a high-voltage source or power pack 24 the other terminal ofwhich is grounded. Received in the front end of the'tube 13 is a plug 26supporting a brush 27 which is connected to the front end of theresistor 21 and makes electrical contact with the nozzle 16.

' The nozzle 16 shown is in the form of a cylindrical body, preferablyof insulating material, having a rearwardly opening, axially disposedrecess 30 adapted to receive the front end of the tube 12. The front endof the nozzle has an elongated outlet orifice 31, desirably of agenerally lenticular form when viewed axially of the nozzle, as in'FIG.2. Such an opening may conveniently be formed by providing the recess 30with a generally hemispherical forward end surface 32 intersected by agroove 33 of V-shaped cross section extending diametrically across thefront end of the nozzle. While the size and proportions of the orifice31 may vary, a suitable orifice has a length approximately equal to thediameter of the hemispherical surface 32 and a width of approximatelyone-sixth that length. Outwardly beyond the extreme forward end of therecess 30, the walls of the groove 33 may be, and preferably are,parallel.

As previously indicated, when a gaseous suspension of powder isdischarged from an orifice such as that described, it will be found thatthe powder is largely concentrated close to the center of the dischargedfan-shaped spray. To obtain a more uniform distribution of powderlaterally of the spray, the nozzle 16 is provided with a pin 35extending across the recess 30 a short distance rearwardly from theorifice 31 Generally speaking, the concentration of powder near thecenter of the spray will be reduced as the diameter of the pin 35 isincreased; and it is therefore possible, by employing a pin ofappropriate diameter, to effect almost any desired lateral distributionof powder within the spray.

In most spray-coating operations, whether the sprayed material is aliquid or a powder, the desideratum is the production of a coating ofuniform thickness. Where the surface to be coated is large enough torequire a plurality of passes of the spray, the mostdcsirable spray isone of fan shape having a relatively wide central portion within whichthe distribution of spray particles is reasonably uniform and sideportions in which the number of particles per unit of spray widthprogressively decreases toward the edges of the spray. A nozzle which wehave found to be capable of producing such a spray was of the formillustrated in the drawings and above described and had the followingdimensions:

Diameter of nozzle body 1 Diameter of hemispherical surface 32 9/16"Length oforifice 31 9/16" Width oforifice 31 0.093" Diameter of pin 351/8 Axial spacing ofcentcr of pin from pole ofsurface 32 0.42"

were obtained at spacings between 0.4l and 0.48". Pins 35 of other thancircular cross section have been used and have given satisfactoryresults; but pins having flat upstream faces are not preferred becausesome powders have a tendency to build up on such faces.

in the gun shown in FIGS. 1-3, electrical charges are imparted to thesprayed particles through the medium of an electrode in the form ofsemiconductive coating 37 of low effective capacity applied to thecylindrical outer surface of the nozzle 16 and connected to the frontend of the resistor 21 through the flexible brush 27, which engages thecoating 37 when the nozzle is in place. As explained in US. LettersPatent No. 3,048,498 granted. Aug. 7, 1962 on the application of J .W..luvinall, et al., the use of the resistor 21 and reduction in theeffective electrical capacity of conductive parts, including theelectrode connected to the high-voltage source preferably glass-filledTeflon or similar resin characterized by relatively high lubricity. Sucha'material, as compared with resins otherwise suitable, has relativelygood wearing properties and little tendency to acquire built-up coatingsof the powder. If the gun is to discharge relatively abrasive material,

such as tale for example, the pin 35, and even the body of the nozzlemay be made of a ceramic to increase resistance to wear. No advantage,by way of charging spray particles, flows from using a pin of conductivematerial and connecting it to the high-voltage source.

In the gun shown in FIGS. l3, the forward edge of the coating 37 servesas a discharge electrode, the spray particles acquire their electricalcharges by bombardment with atmospheric ions generated adjacent thatedge and projected therefrom toward the grounded article being coated,and the charged particles are attracted to such article by electrostaticforces inknown manner. We have found that the efficiency of deposition,or the ratio of powder deposited to powder sprayed, attainable with anozzlesuch as is shown in FIGS. 1- 3 and above described is relativelyconstant over the range of spraying distances (about 3 inches to aboutQinches) normally maintained in practice between the gun and the articlebeing coated. We have further found that the efficiency of depositioncan be measurably increased by providing the nozzle 16 with certainforms of auxiliary electrodes now to be described.

In the arrangement shown in FIG. 4, the auxiliary electrode 40 is a flatpiece of thin sheet metal seated centrally in the groove 33 (See FIG.3), projecting forwardly therefrom, and desirably terminating in acurved front edge as shown. Such an electrode may conveniently be heldin place by two rearwardly projecting, integral fingers 41 which snuglyreceive the nozzle body between them and engage the coating 37.Stainless steel 0.002" in thickness is a suitable material for theelectrode 40. Such an electrode has been found to effect a significantincrease in deposition efficiencies, particularly at spraying distancesin the range from about inches to about inches, but has a disadvantagein that it possesses a relatively high effective electrical capacity andtends to acquire a surface coating when certain powders are sprayed.

The auxiliary electrode 43 shown in FIG. 5 is in the form of a disc ofinsulating material mounted on the nozzle 16 and having a forwardlyprojecting rim disposed to be approximately coplanar with the base ofthe groove 33. A semiconductive coating 44 contacting the coating 37 onthe nozzle body extends over the rear face of the electrode to theperipheral edge thereof. Such an electrode 3 V4 in diameter mounted on anozzle 1'' in diameter significantly increased deposition efficiencies,particularly at spraying distances from about 4" to about 11''.Electrodes 43-44 of smaller diameter also increased depositionefficiencies, but to a lesser degree.

An auxiliary electrode projecting forwardly from the front face of thenoule beside the discharged spray has not been found efiective toincrease deposition efficiency significantly. The same is true of twosuch electrodes located on opposite sides of the spray, and also true ofa fine wire electrode supported on a conductive pin 35 and projectingforwardly through and beyond the orifice 31.

The various auxiliary electrodes above referred to were employed onnozzles 16 of insulating material provided with the pin 35 and asemiconductive coating 37 extending to the periphery of the front nozzleface. Nozzles so coated and used without auxiliary electrodes produceddeposition efficiencies as high as, and in some cases higher than,uncoated nozzles of insulating material provided with electrodes ofother forms. Extending the semiconductive coating over the walls of thegroove 33 did not increase the deposition efficiency. At shorterspraying distances, a nozzle 16 of the type shown and above describedbut formed of metal produced a deposition efficiency slightly higherthan that obtained with a similar nozzle fonned of insulating materialand provided with the semiconductive coating 37; but at sprayingdistances greater than about 7", the latter nozzle was significantlysuperior.

The comparative deposition efficiency results referred to above were allobtained with a spray gun of the form shown in FIG. 1 in which theoutput voltage of the power pack 24 was kv. and the resistance in theoutput circuit, including the resistances of the coating 37, theresistor 21, and a second resistor (not shown) in the power pack, wasabout 450 megohms. Those values for resistance and applied voltage arewithin the range conventionally employed in using electrostatic sprayguns.

We claim as our invention:

1. In a powder-coating apparatus having a spray-discharging nozzleprovided with an elongated outlet orifice, a supply passage leading tosuch orifice, and means for delivering to such passage a gaseoussuspension of powder to be discharged from the orifice as a fanlikespray; means for controlling the lateral distribution of powder withinthe spray, said means including a pin extending across said passagetransversely to the flow therein in a position substantially coplanarwith said oritice and spaced a short distance rearwardly therefrom.

2. Powder-coating apparatus as set forth in claim 1 wherein said orificeis of a generally lenticular shape as viewed axially of said passage.

3. Powder-coating apparatus as set forth in claim 2 wherein said orificeis defined by the intersection of a generally hemispherical surface atthe end of the passage with a groove of V- shaped cross sectionextending across the front face of the nozzle.

4. Powder-coating apparatus as set forth in claim 2 wherein said orificehas a maximum width approximately one-sixth its length and said pin hasa diameter greater than the maximum orifice-width.

5. Powder-coating apparatus as set forth in claim 2 wherein said orificehas a maximum width approximately one-sixth its length.

6. Powder-coating apparatus as set forth in claim 1 wherein said pin isof circular cross section and of uniform diameter throughout thediameter of said passage.

7. Powder-coating apparatus as set forth in claim 1 wherein said pin isof circular cross section.

8. Powder-coating apparatus as set forth in claim 1 wherein the nozzleis formed of electricallyinsulating material and provided with adischarge electrode surrounding said orifice an connected to a source ofhigh voltage.

9. Powder-coating apparatus as set forth in claim 8 wherein thedischarge electrode is the forward edge of a semiconductive coatingapplied to the sides of the nozzle, said coating being connected to thehigh-voltage source through a substantial resistance.

l0. Powder-coating apparatus as set forth in claim 8 with the additionof an annular auxiliary electrode which is of larger diameter than thenozzle and surrounds it.

11. Powder-coating apparatus as set forth in claim 8 with the additionof a thin, platelike auxiliary electrode located in said orifice andprojecting forwardly therefrom.

12. A spray discharging nozzle for. discharging a suspension of coatingmaterial particles in a gaseous medium provided with an elongated outletorifice, said orifice being formed at the intersection of a bore havingconverging walls inside of the nozzle and a notch on the outside of thenozzle, and means within the bore spaced rearwardly from the orifice forcontrolling the lateral distribution of the powder discharged from thenozzle, said means having a surface extending transversely of the boreto intercept and deflect laterally a portion of the flowing suspension.

13. A nozzle as set forth in claim 12 wherein the converging walls ofthe interior bore are spherical at the front of the bore and saidoutside notch is V-shaped.

14. A nozzle as set forth in claim 12 wherein said means for controllingthe lateral distribution of the powder discharged from the nozzle is apin extending transversely of the bore and spaced a short distancerearwardly from the orifice.

15. In a powder spraying apparatus, anelongated conduit for delivering asuspension of powder in a gaseous medium, a nozzle having an elongatedoutlet orifice at the end of said conduit, said nozzle including meansadjacent the orifice inside of the noule to force a convergence ofpowder and gaseous medium at the orifice, and means in the flow of thesuspension and spaced a short distance rearwardly from the orificecooperating with said other means to control the lateral distribution ofpowder discharged from the nozzle.

16. In a powder spraying apparatus, a nozzle for spraying powdersuspended in a gaseous medium, the nozzle comprising,

a body,

a passage in the body adapted to be connected to means for deliveringthe powder suspended in the gaseous medium to the passage, the passageterminating in a forward end surface to force a convergence of thepowder and the gaseous medium,

an outlet orifice in the body communicating with the passage, the outletorifice providing an opening adapted to emit the powder and the gaseousmedium, and

means in the passage assisting in the distribution of the powder withinthe gaseous medium whereby the spray emitted through the outlet orificeincludes a relatively wide central portion wherein the distribution ofpowder is reasonably uniform.

17. A powder spraying nozzle comprising a body having an elongatedorifice at the front of the body and interior walls defining apassageway therethrough for transmitting a flowing suspension of powderin gas to the orifice, means spaced rearwardly of the orifice and actingwithin the body to deflect the flowing suspension,

the walls within said passageway converging forwardly of said means andadjacent the elongated orifice and cooperating with said means toproject the deflected flowing suspension through the elongated orificeas an expanding fan-shaped powder spray with a uniform powderdistribution.

18. A powder nozzle to spray a flowing suspension of powder and gas asan expanding fanlike spray with uniform powder distribution comprising abody having interior walls defining a passageway for the flowingsuspension and an elongated orifice in the forward portion of the bodyadjacent the forward portion of the passageway to emit the spray, thewalls of the passageway having a converging portion adjacent theelongated orifice, and i means spaced rearwardly of the orifice and aconverging portion of the passageway and acting within the passageway todeflect the flowing suspension and in cooperation with the conver ingportion of the walls to distribute the powder uniformfiy within theexpanding fanlike spray.

19. A spray nozzle adapted to be connected to a gaseous suspension ofpowder, the spray nozzle comprising an elongated opening, a passageleading to the opening and adapted to be connected to the gaseoussuspension of powder, the gaseous suspension of powder to be dischargedfrom the opening as a fanlike spray, means in the form of a surface inthe passage and spaced a short distance from the opening and extendinginto the passage to intercept and deflect a portion of the gaseoussuspension of powder and cooperating with the opening to control thedistribution of the powder in the spray.

20. The spray nozzle of claim 19, wherein the surface is substantiallycoplanar with the longest dimension of the opening.

21. The spray nozzle of claim 20, wherein the surface is part of a pin.

22. A spray discharging nozzle for discharging a suspension of coatingmaterial particles in a gaseous medium provided with an elongatedorifice, said orifice being formed at the intersection of a bore havingconverging walls inside of the nozzle and a notch on the outside of thenozzle, a pin extending transversely of the bore and spaced a shortdistance rearwardly from the orifice to intercept and effect laterally aportion of the flowing suspension, the pin being substantially parallelto the length dimension of the orifice and with the orifice controllingthe lateral distribution of the powder discharged from the nozzle.

1. In a powder-coating apparatus having a spray-discharging nozzleprovided with an elongated outlet orifice, a supply passage leading tosuch orifice, and means for delivering to such passage a gaseoussuspension of powder to be discharged from the orifice as a fanlikespray; means for controlling the lateral distribution of powder withinthe spray, said means including a pin extending across said passagetransversely to the flow therein in a position substantially coplanarwith said orifice and spaced a short distance rearwardly therefrom. 2.Powder-coating apparatus as set forth in claim 1 wherein said orifice isof a generally lenticular shape as viewed axially of said passage. 3.Powder-coating apparatus as set forth in claim 2 wherein said orifice isdefined by the intersection of a generally hemispherical surface at theend of the passage with a groove of V-shaped cross section extendingacross the front face of the nozzle.
 4. Powder-coating apparatus as setforth in claim 2 wherein said orifice has a maximum width approximatelyone-sixth its length and said pin has a diameter greater than themaximum orifice-width.
 5. Powder-coating apparatus as set forth in claim2 wherein said orifice has a maximum width approximately one-sixth itslength.
 6. Powder-coating apparatus as set forth in claim 1 wherein saidpin is of circular cross section and of uniform diameter throughout thediameter of said passage.
 7. Powder-coating apparatus as set forth inclaim 1 wherein said pin is of circular cross section.
 8. Powder-coatingapparatus as set forth in claim 1 wherein the nozzle is formed ofelectrically insulating material and provided with a discharge electrodesurrounding said orifice and connected to a source of high voltage. 9.Powder-coating apparatus as set forth in claim 8 wherein the dischargeelectrode is the forward edge of a semiconductive coating applied to thesides of the nozzle, said coating being connected to the high-voltagesource through a substantial resistance.
 10. Powder-coating apparatus asset forth in claim 8 with the addition of an annular auxiliary electrodewhich is of larger diameter than the nozzle and surrounds it. 11.Powder-coating apparatus as set forth in claim 8 with the addition of athin, platelike auxiliary electrode located in said orifice andprojecting forwardly therefrom.
 12. A spray discharging nozzle fordischarging a suspension of coating material particles in a gaseousmedium provided with an elongated outlet orifice, said orifice beingformed at the intersection of a bore having converging walls inside ofthe nozzle and a notch on the outside of the nozzle, and means withinthe bore spaced rearwardly from the orifice for controlling the lateraldistribution of the powder discharged from the nozzle, said means havinga surface extending transversely of the bore to intercept and deflectlaterally a portion of the flowing suspension.
 13. A nozzle as set forthin claim 12 wherein the converging walls of the interior bore arespherical at the front of the bore and said outside notch is V-shaped.14. A nozzle as set forth in claim 12 wherein said means for controllingthe lateral distribution of the powder discharged from the nozzle is apin extending transversely of the bore and spaced a short distancerearwardly from the orifice.
 15. In a powder spraying apparatus, anelongated conduit for delivering a suspension of powder in a gaseousmedium, a nozzle having an elongated outlet orifice at the end of saidconduit, said nozzle including means adjacent the orifice inside of thenozzle to force a convergence of powder and gaseous medium at theorifice, and means in the flow of the suspension and spaced a shortdistance rearwardly from tHe orifice cooperating with said other meansto control the lateral distribution of powder discharged from thenozzle.
 16. In a powder spraying apparatus, a nozzle for spraying powdersuspended in a gaseous medium, the nozzle comprising, a body, a passagein the body adapted to be connected to means for delivering the powdersuspended in the gaseous medium to the passage, the passage terminatingin a forward end surface to force a convergence of the powder and thegaseous medium, an outlet orifice in the body communicating with thepassage, the outlet orifice providing an opening adapted to emit thepowder and the gaseous medium, and means in the passage assisting in thedistribution of the powder within the gaseous medium whereby the sprayemitted through the outlet orifice includes a relatively wide centralportion wherein the distribution of powder is reasonably uniform.
 17. Apowder spraying nozzle comprising a body having an elongated orifice atthe front of the body and interior walls defining a passagewaytherethrough for transmitting a flowing suspension of powder in gas tothe orifice, means spaced rearwardly of the orifice and acting withinthe body to deflect the flowing suspension, the walls within saidpassageway converging forwardly of said means and adjacent the elongatedorifice and cooperating with said means to project the deflected flowingsuspension through the elongated orifice as an expanding fan-shapedpowder spray with a uniform powder distribution.
 18. A powder nozzle tospray a flowing suspension of powder and gas as an expanding fanlikespray with uniform powder distribution comprising a body having interiorwalls defining a passageway for the flowing suspension and an elongatedorifice in the forward portion of the body adjacent the forward portionof the passageway to emit the spray, the walls of the passageway havinga converging portion adjacent the elongated orifice, and means spacedrearwardly of the orifice and a converging portion of the passageway andacting within the passageway to deflect the flowing suspension and incooperation with the converging portion of the walls to distribute thepowder uniformly within the expanding fanlike spray.
 19. A spray nozzleadapted to be connected to a gaseous suspension of powder, the spraynozzle comprising an elongated opening, a passage leading to the openingand adapted to be connected to the gaseous suspension of powder, thegaseous suspension of powder to be discharged from the opening as afanlike spray, means in the form of a surface in the passage and spaceda short distance from the opening and extending into the passage tointercept and deflect a portion of the gaseous suspension of powder andcooperating with the opening to control the distribution of the powderin the spray.
 20. The spray nozzle of claim 19, wherein the surface issubstantially coplanar with the longest dimension of the opening. 21.The spray nozzle of claim 20, wherein the surface is part of a pin. 22.A spray discharging nozzle for discharging a suspension of coatingmaterial particles in a gaseous medium provided with an elongatedorifice, said orifice being formed at the intersection of a bore havingconverging walls inside of the nozzle and a notch on the outside of thenozzle, a pin extending transversely of the bore and spaced a shortdistance rearwardly from the orifice to intercept and effect laterally aportion of the flowing suspension, the pin being substantially parallelto the length dimension of the orifice and with the orifice controllingthe lateral distribution of the powder discharged from the nozzle.